Aggregates coming from different plants are used as substitutes of mineral aggregates for the creation of lightweight and insulating concrete, efficient either on an environmental or on a technical point of view. In France, the most used vegetal aggregates are hemp shiv, corresponding to the woody core part of the stalks of the plant. The oldest construction has been made in 1986. Many studies have been performed in order to characterize the base materials, the properties of the hemp concretes and their functioning in a building. However, to promote the use of these materials, their durability must be guaranteed: hemp shiv contains cellulose and lignin molecules and their microstructure is highly porous. Thus, it is sensible to humidity and hemp concrete can undergo an aging process in humid environments. These durability problems can be associated with a reduction of mechanical, thermal or acoustical properties due to an alkali attack of hemp shivs, vegetal particles mineralization or swelling due to water absorption, the development of micro organisms… The purpose of this study is to highlight the influence of wetting-drying cycles on the mechanical and thermal properties of hemp concretes, and to understand these evolutions by studying the physico-chemical properties and the microstructure of the materials.
